class Mongo::Cursor

Client-side representation of an iterator over a query result set on the server.

A Cursor is not created directly by a user. Rather, CollectionView creates a Cursor in an Enumerable module method.

@example Get an array of 5 users named Emily.

users.find({:name => 'Emily'}).limit(5).to_a

@example Call a block on each user doc.

users.find.each { |doc| puts doc }

@note The Cursor API is semipublic. @api semipublic

Attributes

resume_token[R]

The resume token tracked by the cursor for change stream resuming

@return [ BSON::Document | nil ] The cursor resume token. @api private

server[R]

@api private

view[R]

@return [ Collection::View ] view The collection view.

Public Class Methods

finalize(cursor_id, cluster, op_spec, server, session) click to toggle source

Finalize the cursor for garbage collection. Schedules this cursor to be included in a killCursors operation executed by the Cluster's CursorReaper.

@example Finalize the cursor.

Cursor.finalize(id, cluster, op, server)

@param [ Integer ] cursor_id The cursor's id. @param [ Mongo::Cluster ] cluster The cluster associated with this cursor and its server. @param [ Hash ] op_spec The killCursors operation specification. @param [ Mongo::Server ] server The server to send the killCursors operation to.

@return [ Proc ] The Finalizer.

@since 2.3.0

# File lib/mongo/cursor.rb, line 104
def self.finalize(cursor_id, cluster, op_spec, server, session)
  proc do
    cluster.schedule_kill_cursor(cursor_id, op_spec, server)
    session.end_session if session && session.implicit?
  end
end
new(view, result, server, options = {}) click to toggle source

Creates a Cursor object.

@example Instantiate the cursor.

Mongo::Cursor.new(view, response, server)

@param [ CollectionView ] view The CollectionView defining the query. @param [ Operation::Result ] result The result of the first execution. @param [ Server ] server The server this cursor is locked to. @param [ Hash ] options The cursor options.

@option options [ true, false ] :disable_retry Whether to disable

retrying on error when sending getMore operations (deprecated, getMore
operations are no longer retried)

@option options [ true, false ] :retry_reads Retry reads (following

the modern mechanism), default is true

@since 2.0.0

# File lib/mongo/cursor.rb, line 68
def initialize(view, result, server, options = {})
  @view = view
  @server = server
  @initial_result = result
  @remaining = limit if limited?
  @cursor_id = result.cursor_id
  @coll_name = nil
  @options = options
  @session = @options[:session]
  register
  if @cursor_id && @cursor_id > 0
    ObjectSpace.define_finalizer(self, self.class.finalize(@cursor_id,
      cluster,
      kill_cursors_op_spec,
      server,
      @session))
  end
end

Public Instance Methods

batch_size() click to toggle source

Get the batch size.

@example Get the batch size.

cursor.batch_size

@return [ Integer ] The batch size.

@since 2.2.0

# File lib/mongo/cursor.rb, line 223
def batch_size
  @view.batch_size && @view.batch_size > 0 ? @view.batch_size : limit
end
closed?() click to toggle source

Is the cursor closed?

@example Is the cursor closed?

cursor.closed?

@return [ true, false ] If the cursor is closed.

@since 2.2.0

# File lib/mongo/cursor.rb, line 235
def closed?
  !more?
end
collection_name() click to toggle source

Get the parsed collection name.

@example Get the parsed collection name.

cursor.coll_name

@return [ String ] The collection name.

@since 2.2.0

# File lib/mongo/cursor.rb, line 247
def collection_name
  @coll_name || collection.name
end
each() { |document| ... } click to toggle source

Iterate through documents returned from the query.

@example Iterate over the documents in the cursor.

cursor.each do |doc|
  ...
end

@return [ Enumerator ] The enumerator.

@since 2.0.0

# File lib/mongo/cursor.rb, line 133
def each
  # If we already iterated past the first batch (i.e., called get_more
  # at least once), the cursor on the server side has advanced past
  # the first batch and restarting iteration from the beginning by
  # returning initial result would miss documents in the second batch
  # and subsequent batches up to wherever the cursor is. Detect this
  # condition and abort the iteration.
  #
  # In a future driver version, each would either continue from the
  # end of previous iteration or would always restart from the
  # beginning.
  if @get_more_called
    raise NotImplementedError, 'Cannot restart iteration of a cursor which issued a getMore'
  end

  # To maintain compatibility with pre-2.10 driver versions, reset
  # the documents array each time a new iteration is started.
  @documents = nil

  loop do
    document = try_next
    yield document if document
  end
rescue StopIteration => e
  return self
end
get_more() click to toggle source

Execute a getMore command and return the batch of documents obtained from the server.

@return [ Array<BSON::Document> ] The batch of documents

@api private

# File lib/mongo/cursor.rb, line 284
def get_more
  @get_more_called = true

  # Modern retryable reads specification prohibits retrying getMores.
  # Legacy retryable read logic used to retry getMores, but since
  # doing so may result in silent data loss, the driver no longer retries
  # getMore operations in any circumstance.
  # https://github.com/mongodb/specifications/blob/master/source/retryable-reads/retryable-reads.rst#qa
  process(get_more_operation.execute(@server))
end
id() click to toggle source

Get the cursor id.

@example Get the cursor id.

cursor.id

@note A cursor id of 0 means the cursor was closed on the server.

@return [ Integer ] The cursor id.

@since 2.2.0

# File lib/mongo/cursor.rb, line 261
def id
  @cursor_id
end
inspect() click to toggle source

Get a human-readable string representation of Cursor.

@example Inspect the cursor.

cursor.inspect

@return [ String ] A string representation of a Cursor instance.

@since 2.0.0

# File lib/mongo/cursor.rb, line 119
def inspect
  "#<Mongo::Cursor:0x#{object_id} @view=#{@view.inspect}>"
end
to_return() click to toggle source

Get the number of documents to return. Used on 3.0 and lower server versions.

@example Get the number to return.

cursor.to_return

@return [ Integer ] The number of documents to return.

@since 2.2.0

# File lib/mongo/cursor.rb, line 274
def to_return
  use_limit? ? @remaining : (batch_size || 0)
end
try_next() click to toggle source

Return one document from the query, if one is available.

This method will wait up to max_await_time_ms milliseconds for changes from the server, and if no changes are received it will return nil. If there are no more documents to return from the server, or if we have exhausted the cursor, it will raise a StopIteration exception.

@note This method is experimental and subject to change.

@return [ BSON::Document | nil ] A document. @api private

# File lib/mongo/cursor.rb, line 172
def try_next
  if @documents.nil?
    # Since published versions of Mongoid have a copy of old driver cursor
    # code, our dup call in #process isn't invoked when Mongoid query
    # cache is active. Work around that by also calling dup here on
    # the result of #process which might come out of Mongoid's code.
    @documents = process(@initial_result).dup
    # the documents here can be an empty array, hence
    # we may end up issuing a getMore in the first try_next call
  end

  if @documents.empty?
    # On empty batches, we cache the batch resume token
    cache_batch_resume_token

    if more?
      if exhausted?
        kill_cursors
        raise StopIteration
      end
      @documents = get_more
    else
      raise StopIteration
    end
  else
    # cursor is closed here
    # keep documents as an empty array
  end

  # If there is at least one document, cache its _id
  if @documents[0]
    cache_resume_token(@documents[0])
  end

  # Cache the batch resume token if we are iterating
  # over the last document, or if the batch is empty
  if @documents.size <= 1
    cache_batch_resume_token
  end

  return @documents.shift
end

Private Instance Methods

cache_batch_resume_token() click to toggle source
# File lib/mongo/cursor.rb, line 307
def cache_batch_resume_token
  @resume_token = @post_batch_resume_token if @post_batch_resume_token
end
cache_resume_token(doc) click to toggle source
# File lib/mongo/cursor.rb, line 301
def cache_resume_token(doc)
  if doc[:_id] && doc[:_id].is_a?(Hash)
    @resume_token = doc[:_id] && doc[:_id].dup.freeze
  end
end
end_session() click to toggle source
# File lib/mongo/cursor.rb, line 330
def end_session
  @session.end_session if @session && @session.implicit?
end
exhausted?() click to toggle source
# File lib/mongo/cursor.rb, line 297
def exhausted?
  limited? ? @remaining <= 0 : false
end
get_more_operation() click to toggle source
# File lib/mongo/cursor.rb, line 311
def get_more_operation
  if @server.features.find_command_enabled?
    spec = Builder::GetMoreCommand.new(self, @session).specification
  else
    spec = Builder::OpGetMore.new(self).specification
  end
  Operation::GetMore.new(spec)
end
kill_cursors() click to toggle source
# File lib/mongo/cursor.rb, line 320
def kill_cursors
  unregister
  read_with_one_retry do
    kill_cursors_operation.execute(@server)
  end
ensure
  end_session
  @cursor_id = 0
end
kill_cursors_op_spec() click to toggle source
# File lib/mongo/cursor.rb, line 338
def kill_cursors_op_spec
  if @server.features.find_command_enabled?
    Builder::KillCursorsCommand.new(self).specification
  else
    Builder::OpKillCursors.new(self).specification
  end
end
kill_cursors_operation() click to toggle source
# File lib/mongo/cursor.rb, line 334
def kill_cursors_operation
  Operation::KillCursors.new(kill_cursors_op_spec)
end
limit() click to toggle source
# File lib/mongo/cursor.rb, line 376
def limit
  @view.send(:limit)
end
limited?() click to toggle source
# File lib/mongo/cursor.rb, line 346
def limited?
  limit ? limit > 0 : false
end
more?() click to toggle source
# File lib/mongo/cursor.rb, line 350
def more?
  @cursor_id != 0
end
process(result) click to toggle source
# File lib/mongo/cursor.rb, line 354
def process(result)
  @remaining -= result.returned_count if limited?
  @coll_name ||= result.namespace.sub("#{database.name}.", '') if result.namespace
  unregister if result.cursor_id == 0
  @cursor_id = result.cursor_id

  if result.respond_to?(:post_batch_resume_token)
    @post_batch_resume_token = result.post_batch_resume_token
  end

  end_session if !more?

  # Since our iteration code mutates the documents array by calling #shift
  # on it, duplicate the documents here to permit restarting iteration
  # from the beginning of the cursor as long as get_more was not called
  result.documents.dup
end
register() click to toggle source
# File lib/mongo/cursor.rb, line 380
def register
  cluster.register_cursor(@cursor_id)
end
unregister() click to toggle source
# File lib/mongo/cursor.rb, line 384
def unregister
  cluster.unregister_cursor(@cursor_id)
end
use_limit?() click to toggle source
# File lib/mongo/cursor.rb, line 372
def use_limit?
  limited? && batch_size >= @remaining
end